SRD:Ring of Force Shield

From D&D Wiki

Force Shield: An iron band, this simple ring generates a shield-sized (and shield-shaped) wall of forcethat stays with the ring and can be wielded by the wearer as if it were a heavy shield (+2 AC). This special creation has no armor check penalty or arcane spell failure chance since it is weightless and encumbrance-free. It can be activated and deactivated at will as a free action.